Experimental study on influence of immersion times on rock strength and failure characteristics

A thorough investigation into time-dependent water-rock interactions is of significant importance for the prevention and control of engineering instability disasters. In this study, laboratory uniaxial compression tests, Brazilian splitting tests, and direct shear tests were conducted on sandstone, marble and granite specimens with immersion times of 30, 90 and 180 d, respectively, to explore and reveal the characteristics and mechanisms of the effects of different immersion times on the strength and failure characteristics of rock masses. The results show that after immersion, the mechanical strength of sandstone specimens decreases significantly, and the decreasing trend gradually slows with increasing immersion time. In contrast, the compressive strength of marble and granite specimens decreases significantly after 30 d of immersion, but shows an increasing trend after 90 d of immersion, followed by a subsequent decrease. Similar trends are observed for their shear strength. These changes may be due to the dissolution and weakening of the cement between mineral particles inside the rock, coupled with the local strengthening of strength under non-draining conditions of water-saturated pores inside the rock mass. Analysis of the energy characteristics of the specimens revealed that the total input strain energy and elastic strain energy(stored energy capacity) of sandstone and granite specimens both show a decreasing trend after immersion, while the change in marble specimens is not significant. This suggests a reduced severity of ejection failure in granite specimens after immersion. Based on these findings, a shear brittleness index(<italic>B</italic>_s) was proposed to evaluate the brittleness characteristics of rock joints. The study found that with increasing immersion time, the brittleness of sandstone, marble and granite joints all show a decreasing trend. The results of this study can provide important references for evaluating the stability of engineering rock masses under water-rock interactions.